Rod, The rules are not on the WKA website you must buy the 2004 tech manual. Here is the rules on the head.
708.19 cylinder head- stock B&S head part#558 AS SHIPPED FROM FACTORY. Machining of gasket surface ONLY allowed.NO MACHINING OF PORTS ALLOWED
708.19.1 -depth of head at shallow part of head .016″Min. Depth at floor of head .324″ Min.
708.19.2 Depth to top of valve seat:.360″ max .340″ min.
I WILL HAVE COPIES OF THE WKA STOCK ANIMAL RULES#708 W/ THE AMENDED RULES FOR THE LIM.MOD CLASS AT THE FIRST RACE AT IMI FOR ALL PARTICIPANTS IN THIS CLASS. SEE YA AT THE RACES………..GREG